The present invention relates to an ignition timing control system for an automotive engine with a time control system.
Japanese Patent Application Laid-Open No. 60-85256 discloses an ignition timing control system with a time control system.
In the ignition timing control system, a rotor disk is provided for rotating in synchronism with a crankshaft of the engine, and position indicator means, such as projections on the periphery of the disk, are provided at every position corresponding to predetermined crank angles. A sensor is mounted adjacent the rotor disk for producing a crank angle signal at the position of the indicator means in the form of a pulse. The pulse signal is applied to an electronic control unit comprising a microcomputer. The control unit detects the pulse spacing time T and pulse spacing crank angle .theta.. On the other hand, an ignition angle .theta..sub.SPK is derived from a map in accordance with engine speed and engine load. An ignition timing T.sub.SPK is calculated as follows. EQU T.sub.SPK =T/.theta..times..theta..sub.SPK
However, the microcomputer takes time to perform the division in the above equation.
Consequently, the time for calculating the ignition timing is reduced by the time for the division. Therefore, the ignition timing can not be properly controlled. In order to overcome this defect, a microcomputer having a large capacity must be used, which increases a manufacturing cost.